1. Field
One embodiment of the invention relates to a transmitter, a receiver, and a transmitting method which transmits or receives a variety of contents requiring copyright protection.
2. Description of the Related Art
With the spread of a computer network, such as a broadband and a wireless LAN, and with the progress of a digital technique, a product called digital information appliance (hereinafter referred to as digital household electric appliance) with a communication function has become widely used. As a terrestrial digital broadcasting has started, in the future, more diffusion of television receivers, set top boxes, DVD recorders, etc., corresponding to a digital broadcasting are predicted. Connecting a plurality of digital household electric appliances allows a user to enjoy content via a network and put the appliances to good use.
Here, contents include a variety of items of digital data, for instance, motion image data and audio data such as MPEG-2 and MPEG-4, and document data such as text data and image data. While one hand the content including the digital data of this type has an advantage in that it can be easily copied without any deterioration, it has to be paid attention in regard to copyright thereof. For example, it is assumed that the content the copyright of which should be protected is moved from a transmitter to a receiver. When the content requiring its copyright protection is moved, it is desirable for the content which has transmitted to the receiver to be moved without being remained in the transmitter, and without being copied in a plain text on a communication path to any device other than the receiver. A means for preventing copying the content on the communication path includes a method of sharing a key between the transmitter and receiver, and encrypting the content with the key to transmit it (refer to DTCP-IP specifications “DTCP. Volume 1, Supplement E, Mapping DTCP to Ip (Information Version)” (http://www.dtcp.com).
From the point of view of efficiency of a communication, contents are further efficient to be encrypted with the same key for a model in a multicast or broadcast to simultaneously distribute the identical contents from the transmitter to a plurality of receivers. Therefore, a situation in which the plurality of receivers share the same key occurs. However, moving the contents with the keys distributed to the plurality of receivers allows the plurality of receivers to decode the contents to be moved, so that the moving of the contents is not performed normally.
Like this, the occurrence of a situation in which the moving of the contents is not executed normally and their copyrights are not protected is possible in a conventional content transmitting/receiving system.